Negative electric plates for alkaline accumulators and methods for making same



2,683,181 UMULATORS July 6, 1954 .1. SALAUZE NEGATIVE ELECTRIC PLATES FOR ALKALINE ACC AND METHODS FOR MAKING SAME Filed April 27, 1955 PRO v/w/ve SUBSTANCE J/A/TER/A/G 601 5)? (3/? Y5 TA JEAN ALAUZE INVENTOR.

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Patented July 6, 1954 UNITED STATES ATEN T OFFICE NEGATIVE ELECTRIC PLATES FOR ALKA- LINE. ACCUMULATORS AND METHODS FOR MAKING SAME Application April 27, 1953, Serial No. 351,479

Claims priority, application France December 14, 1950 7 Claims.

This application is a continuation-in-part of my co-pending application Ser. No. 207,237, filed January 22, 1951 (now U. S. Patent No. 2,643,276, issued June 23, 1953).

In said co-pending application a method has been described aiming at the manufacture of negative electric plates for alkaline storage batteries. According to this former method, the plate is formed of a basic material which is copper in finely divided condition consisting of minute acicular, dendritic or arborescent crystals, said copper being thoroughly mixed with pulverulent iron or an iron. providing compound adapted to produce iron when the battery is being charged, said iron or iron providing substance being used as the active elements of the plate. The mixture is compressed under a relatively high pressure on suitable frames embedded in it.

The compression and the simultaneous interlacing action of the copper crystals result in the formation of a coherent and porous solid structure including the iron material, wherein the preferably perforated frame acts as a supporting srtucture and as a conductor.

In a second co-pending application Serial No. 351,480, filed concurrently herewith, a few forms or embodiments of the above method have been described. More particularly it has been stated that the active substance could consist of pure iron or of magnetic oxide or of a mixture of both, provided they have a low density and high porosity.

As set forth in these two co-pending applications, the compression applied must be very high. It must attain at least 1 ton/ sq. cm. and can exceed, without any inconvenience, 3 tons/sq. cm., the results improving as this upper end of the range is approached. These improved results are observed as regards not only the electrical efiiciency of the plates but also the mechanical resistance thereof during the various handlings to which they are subjected from the time they are manufactured to that when their fitting inside battery cells is completed, these handlings being frequently attended by carelessness and the absence of suitable precautions.

A disadvantage in these applications is that the required use of very high pressures requires powerful and costly presses.

One of the objects of the present invention is to reduce to a certain extent the required pressures used in these methods while yielding as a final product, battery plates having the desired electrical characteristics and a very good resistance to shocks without scaling off or even local disintegration.

The accompanying drawing is a diagrammatic illustration on a greatly enlarged scale of a fragmentary portion of an electrode plate made in accordance with the methods of this invention and illustrating diagrammatically the struc ture and inter-relationship of the components forming the plate.

The improved method of this invention is characterized in that it consists in subjecting the plates, after they have been shaped by a press, to a thermal treatment, hereinafter termed sintering since its effect is to sinter the copper content of the plates, that is, to bring about between the copper particles by means of superficial coalescence, a system of local bonds obtained through welding.

This sintering is carried out by heating the formed plates to a temperature ranging between 600" and 650 C. While these temperature limits are not limiting or absolute, yet applicant has observed that by heating the plate below 600 C. the sintering was defective and that by heating above 650 C. the electrical characteristics of the plates weakened as the temperature increased.

Of course, the atmosphere of the furnace must be free from oxidizing agents; it should be either neutral or reducing. In practice, nitrogen or hydrogen, or a mixture in variable proportions of both gases may be resorted to. In fact, economical operation is obtained by utilizing nitrogen containing about 10% to 20% of hydrogen.

Continuous or discontinuous sintering furnaces may be used. For mass production, continuous furnaces are more advantageous. The plates, laid upon the conveyor belt of the furnace, pass through the latter and the duration of this passage, which is conditioned above all by the fact that the plate must be nearly cold (usual room temperatures) when discharged from the furnace, may be of the order of from one to several hours. In fact, the time during which the plates are actually subjected to the 600650 C. temperature range may be substantially less than one hour.

This sintering treatment is a source of improvement especially for those plates which have been insufficiently pressed, for instance, under pressures below 1 ton/sq. cm. These plates are rather brittle and prone to spall off during their handling, so that their physical behavior as Well as their electrical characteristicsare substantially improved with this treatment.

In the co-pending applications mentioned above it is explained in an extensive manner that the iron providing substance utilized in admixture with copper in finely divided condition consisting of minute acicular, dendritic or arborescent crystals could have different origins. In practice, regardless of its chemical nature, the iron providing substance is derived from ferric oxide F8203 through thermal reduction by means of hydrogen.

Applicant has found that copper-ferric oxide powder mixtures could be utilized by compressing the same when cold at pressures below 1 ton/sq. cm. on plate metal frames, as described in the co-pending applications. If these plates are passed through a sintering furnace having a reducing atmosphere and heated at about 600-650 C., the ferric oxide undergoes a thermal reduction through the hydrogen and is converted either into iron or into magnetic oxide, or into a mixture of both. While this reduction proceeds, a sintering occurs whereby the copper crystals coalesce together. With this invention, the manufacture of negative plates is made more economical since two steps are merged into one.

The invention is also concerned with the plates obtained by carrying out the above method, as a new article of manufacture.

Of course, the invention is not to be construed as being limited to the sole examples, proportions and values indicated above and given for illustrative purpose only.

What I claim is:

1. In a method of manufacturing negative electric plates for alkaline accumulators comprising the step of mixing together a basic material composed of finely divided copper having the shape of microscopic acicular, arborescent or dendritical crystals with an active material which consists of a finely divided iron or iron providing substance, the step of compressing the said mixture under a high pressure on suitable supporting frames, and the step consisting of subjecting the plates after they have been compressed to a thermal or sintering treatment '4 resulting in the sintering of copper particles and establishing among the copper particles, by superficial coalescence, a system of local welded bonds.

2. A method according to claim 1 wherein the sintering step is carried out at a temperature range of about 600650 0., and in a reducing or neutral atmosphere.

3. The method of claim 1 wherein the thermal or sintering treatment is effected in a reducing atmosphere at a temperature range of about 600-650 C. and wherein said reducing atmosphere consists of a mixture of nitrogen and hy-- drogen, and wherein said treatment is effected for a period that is substantially less than one hour.

4. The method of claim 1 wherein the thermal or sintering treatment is effected by passing the plates through a furnace where a reducing atmosphere is maintained so as to subject the plates to heat in a zone of the furnace in a temperature range of from about 600-650 C. for a period that is substantially less than an hour and removing said plates from the zone when cooled nearly to usual room temperatures.

5. The method of claim 1, wherein the iron providing substance is an iron product obtained by thermal reduction of ferric oxide by hydrogen.

6. A method according to claim 1 wherein the iron providing substance incorporated into the plate at the start is ferric oxide F6203 itself and a sintering treatment is effected in a reducing atmosphere so as to reduce simultaneously the aforesaid ferric oxide to iron products reducible in form to iron state when the battery is being charged.

7. A negative electric plate for alkaline accumulators as obtained by the method of claim 1.

References Cited in the file Of this patent UNITED STATES PATENTS Number 

1. IN A METHOD F MANUFACTURING NEGATIVE ELECTRIC PLATES FOR ALKALINE ACCUMULATORS COMPRISING THE STEPS OF MIXING TOGETHER A BASIC MATERIAL COMPOSED OF FINELY DIVIDED COPPER HAVING THE SHAPE OF MICROSCOPIC ACICULA, ARBORESCENT OR DENDRITICAL CRYSTALS WITH AN ACTIVE MATERIAL WHICH CONSISTS OF A FINELY DIVIDED IRON OR IRON PROVIDING SUBSTANCES, THE STEP OF COMPRESSING THE SAID MIXTURE UNDER A HIGH PRESSURE ON SUITABLE SUPPORTING FRAMES, AND THE STEPS CONSISTING OF SUBJECTING THE PLATES AFTER THEY HAVE BEEN COM- 